[Remoting Mobile] Update What's New Texts

This CL updates the What's New texts to reflect these changes:
* Between Android client M61 and M70
* Between iOS client M67 and M70

Bug: 877704
Change-Id: Ifb3aff593c1bfc3a8b1f02f018dd458670c3100e
Reviewed-on: https://chromium-review.googlesource.com/1189055Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586076}

remoting/resources/remoting_strings.grd

@@ -683,7 +683,7 @@ Remote computers with non US-English keyboards may receive incorrect text input.
 For information about privacy, please see the Google Privacy Policy (http://goo.gl/SyrVzj) and the Chrome Privacy Policy (http://goo.gl/0uXE5d).
         </message>
         <message name="IDS_PLAY_STORE_CHANGES" desc="List of what's changed in this release of Chrome Remote Desktop for Android. [CHAR-LIMIT=500] [NAME=play_store_changes]">
-• Added support for Android 8.0 Oreo.
+• Added support for Android 9.0 Pie.
         </message>
 
         <!-- iOS App Store metadata text. Won't be bundled into the app. -->
@@ -710,7 +710,8 @@ Securely access your computer from your iOS device. It's fast, simple and free.
 • On your iOS device, open the app and tap on any of your online computers to connect.
         </message>
         <message name="IDS_APP_STORE_CHANGES" desc="List of what's changed in this release of Chrome Remote Desktop for iOS. [CHAR-LIMIT=4000] [NAME=app_store_changes]">
-General fixes and stability improvements.
+• Better panning and zooming experience on iPhone X.
+• Stability improvements and bug fixes.
         </message>
       </if>  <!-- is_android or is_ios -->